Cantilever force sensor

ABSTRACT

A cantilever force sensor with relatively lower On-Force is disclosed, which comprises a top stack, a bottom stack, and a spacer. The first spacer is configured between the top stack and the bottom stack and configured in a first side of the force sensor. A second side, opposite to the first side, of the top stack, is cantilevered from the bottom stack. When the force sensor is depressed from the top side, the second side of the top stack moves down using the first spacer as a fulcrum. Since the cantilevered side can be easily depressed down so that the On-Force for the force sensor is reduced and hence a force sensor with a relatively higher sensitivity is created.

RELATED APPLICATION(S)

The instant application is a continuation application of U.S.application Ser. No. 17/152,668, filed Jan. 19, 2021, which isincorporated by reference herein in its entirety.

BACKGROUND Technical Field

The present invention relates to a force sensor, especially relates to acantilever force sensor which can be turned on with a relatively reducedon-force so that a force sensor with higher sensitivity is created.

Description of Related Art

FIGS. 1A˜1D shows a prior art.

Referring to FIG. 1A as disclosed in U.S. Pat. No. 8,371,174, aconventional force sensor comprises a top substrate 10 and a bottomsubstrate 109, a top electrode 11 is configured on a bottom side of thetop substrate 10. A bottom electrode 119 is configured on the top sideof the bottom substrate 109. A top piezoresistive layer 12 is configuredon the bottom side of the top electrode 11. A bottom piezoresistivelayer 129 is configured on the top side of the bottom electrode 119. Aspace 16 is formed between the two piezoresistive layers 12, 129. Asshown in FIG. 1A, a ring spacer 15 is configured between the substrates10 and 109. The top electrode 11 and bottom electrode 119 areelectrically connected to a circuit system 13.

FIG. 1B shows an EE′ section view of the prior art FIG. 1A.

FIG. 1B shows that a ring spacer 15 is configured around the forcesensor. The ring spacer 15 resists more against a force applied from thetop side of the force sensor.

FIG. 1C shows when a force P is applied to the force sensor of FIG. 1A,the top piezoresistive layer 12 deforms downwardly in the middle portionand contacts the bottom piezoresistive layer 129, at this moment, thepiezoresistive layers 12 and 129 have a total thickness of L1. Hence, anoutput resistance R1 of the force sensor can be determined by theequation R1=p*L1/A.

FIG. 1D shows an electricity property for the prior art.

FIG. 1D shows a curve for Conductance/Capacitance vs Force for FIG. 1C.Referring to FIG. 1D a status when the force sensor is depressed fromthe top side, at the moment of FIG. 1C, an On-Force starts at point P1which is apparently greater than the zero force point. This is becausethe ring spacer 15 resists the force applied from the top of the forcesensor.

A disadvantage for the prior art is that an On-Force is relativelygreater because the ring spacer 15 gives more resistance to the forceapplied from the top side. It is hopeful for a person skilled in the artto reduce the On-Force so that a force sensor with a higher sensitivitycan be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A˜1D shows a prior art.

FIGS. 2A˜2D shows a first embodiment according to the present invention.

FIG. 3 shows the first embodiment configured in an electronic penaccording to the present invention.

FIGS. 4A˜4B shows a second embodiment according to the presentinvention.

FIG. 5 shows a third embodiment according to the present invention.

FIG. 6 shows a fourth embodiment according to the present invention.

FIG. 7 shows a fifth embodiment according to the present invention.

FIG. 8 shows a sixth embodiment according to the present invention.

FIG. 9 shows a seventh embodiment according to the present invention.

FIGS. 10A˜10B shows an eighth embodiment according to the presentinvention.

FIGS. 11A˜11B shows a ninth embodiment according to the presentinvention.

FIGS. 12A˜12B shows a tenth embodiment according to the presentinvention.

FIGS. 13A˜13B shows an eleventh embodiment according to the presentinvention.

FIGS. 14A˜14B shows a twelfth embodiment according to the presentinvention.

FIG. 15 shows a thirteenth embodiment according to the presentinvention.

FIG. 16 shows a fourteen embodiment according to the present invention.

FIG. 17 shows a fifteen embodiment according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2A˜2D shows a first embodiment according to the present invention.

FIG. 2A shows a cantilever force sensor FS with a bottom switch SWconfigured on the bottom side of the force sensor FS. The force sensorFS comprises a top stack TS, a first spacer S1, and a bottom stack BS insequence. A first gap G1 is configured between the top stack TS and thebottom stack BS. The first spacer S1 is configured in the right side ofthe force sensor FS. The left side of the top stack TS is cantileveredfrom the bottom stack BS.

When the force sensor FS is depressed from the top side, the left sideof the top stack TS moves down using the first spacer S1 as a fulcrum toturn on the force sensor FS. The first spacer S1 has a top end connectedto the top piezo layer 22 of the top stack TS and has a bottom endconnected to the bottom piezo electrode 24 of the bottom stack BS.

The top stack TS is comprised of a top substrate 20, a top electrode 21,and a top piezo layer 22 in sequence. The bottom stack BS is comprisedof a bottom piezo layer 23, a bottom electrode 24, and a bottomsubstrate 25 in sequence.

A bottom switch SW is configured on the bottom side of the force sensorFS. A first conductive contact C1 is configured on the bottom side ofthe bottom stack BS of the force sensor FS. A second conductive contactC2, aligned with the first conductive contact C1, is configured on a topside of a printed circuit board 26 of the bottom switch SW. A secondspacer S2 is configured between the bottom substrate 25 and the printedcircuit board 26, and the second spacer S2 is configured in the rightside of the bottom switch SW. The bottom stack BS, the first conductivecontact C1, the second conductive contact C2, and the printed circuitboard 26 are configured in sequence to form the bottom switch SW. Thedelayed turn-on switch is designed for shielding the initial noisesignal from the force sensor at an initial stage when it is depressed.

The first conductive contact C1 slightly touches the second conductivecontact C2, however without turns on the bottom switch SW. When theforce sensor FS is depressed from the top side, the left side of theforce sensor FS moves down so that the first conductive contact C1touches the second conductive contact C2 firmly to turn on the bottomswitch SW.

FIG. 2B shows an AA′ section view of FIG. 2A according to the presentinvention. The first spacer S1 is configured in the right side of theforce sensor FS, and configured between the top stack TS and the bottomstack BS of the force sensor FS.

FIG. 2C shows the force sensor being depressed according to the presentinvention. The top stack TS moves down on its left side using the firstspacer S1 as a fulcrum when the force sensor FS is depressed from thetop side. After the top stack TS touches the bottom stack BS, a forcesignal is sent to a control center (not shown) for signal processing.

FIG. 2D shows an electrical property for the first embodiment accordingto the present invention. FIG. 2D shows a curve forConductance/Capacitance vs Force for the first embodiment. Referring toFIG. 2C a status when the force sensor FS is depressed from the topside, an On-Force starts at point P2 which is extremely near to zeroforce point. This is because that a single side spacer S1 is configuredin the right side of the force sensor FS. The cantilevered top stack TSof the force sensor FS reduces On-Force.

FIG. 3 shows the first embodiment configured in an electronic penaccording to the present invention.

FIG. 3 shows that the force sensor FS with a bottom switch SW can beconfigured on the bottom side of the pen tip 61 of an electronic pen tosense forces coming from the pen tip 61 when the electronic pen iswriting with its pen tip 61.

FIGS. 4A˜4B shows a second embodiment according to the presentinvention.

FIG. 4A shows a modified embodiment to the first embodiment of FIG. 2Awith a different position for the first spacer S1. FIG. 4A shows thatthe first spacer S1 is configured between the top stack TS and thebottom stack BS and configured in the right side of the force sensor FS.The spacer S1 has a top end connected to the top substrate 20 and has abottom end connected to the bottom substrate 25.

FIG. 4B shows a BB′ section view of FIG. 4A according to the presentinvention. The first spacer S1 is configured in the right side of theforce sensor FS, and configured between the top stack TS and the bottomstack BS.

FIG. 5 shows a third embodiment according to the present invention.

FIG. 5 shows a further modified embodiment to the first embodiment witha different position for the first spacer S1. The first spacer S1 isconfigured between the top stack TS and the bottom stack BS andconfigured in the right side of the force sensor FS. The spacer S1 has atop end connected to the top piezo layer 22 and has a bottom endconnects to the bottom substrate 25.

FIG. 6 shows a fourth embodiment according to the present invention.

FIG. 6 shows a further modified embodiment to the first embodiment witha different position for the first spacer S 1. The first spacer S1 isconfigured between the top stack TS and the bottom stack BS andconfigured in the right side of the force sensor FS. The spacer S1 has atop end connected to the top substrate 20 and has a bottom end connectedto the bottom piezo layer 23.

FIG. 7 shows a fifth embodiment according to the present invention.

FIG. 7 shows a further modified embodiment of the force sensor FS with amodified bottom switch configured in an electronic pen. The force sensorFS with a bottom switch SW can be configured in the bottom side of thepen tip 61 of an electronic pen to sense forces coming from the pen tip61 when the electronic pen is writing with its pen tip 61. The firstconductive contact C1 under the force sensor FS is configured slightlyapart from the second conductive contact C2. When the force sensor FS isdepressed from the top side, the left side of the bottom stack BS movesdown so that the first conductive contact C1 touches the secondconductive contact C2 firmly to turn on the bottom switch SW. Thedelayed turn-on switch is designed for shielding the initial noisesignal from the force sensor FS at an initial stage when the forcesensor FS is depressed.

FIG. 8 shows a sixth embodiment according to the present invention.

FIG. 8 shows a further modified embodiment to the first embodiment. Asingle piezo layer, a top piezo layer 22, is configured in the forcesensor FS. The top stack TS is comprised of a top substrate 20, a topelectrode 21, and a top piezo layer 22 in sequence. The bottom stack BSis comprised of a bottom electrode 24 and a bottom substrate 25 insequence and without having any piezo layer configured in the bottomstack BS.

The first spacer S1 is configured between the top stack TS and thebottom stack BS and configured in the right side of the force sensor FS.A first gap G1 is configured between the top stack TS and the bottomstack BS. The first spacer S1 has a top end connected to the top piezolayer 22 of the top stack TS and has a bottom end connected to thebottom electrode 24 of the bottom stack BS.

FIG. 9 shows a seventh embodiment according to the present invention.

FIG. 9 shows a modified embodiment to the first embodiment. A singlepiezo layer, a bottom piezo layer 23, is configured in the force sensorFS. The top stack TS is comprised of a top substrate 20, and a topelectrode 21 in sequence. The bottom stack BS is comprised of a bottompiezo layer 23, a bottom electrode 24, and a bottom substrate 25 insequence.

The first spacer S1 is configured between the top stack TS and thebottom stack BS and configured in the right side of the force sensor FS.A first gap G1 is configured between the top stack TS and the bottomstack BS. The first spacer S1 has a top end connected to the topelectrode 21 of the top stack TS and has a bottom end connected to thebottom piezo layer 23 of the bottom stack BS.

FIGS. 10A˜10B shows an eighth embodiment according to the presentinvention.

FIG. 10A shows a modified embodiment to the first embodiment. FIG. 10Ashows a front view of the modified embodiment where a single piezolayer, a bottom piezo layer 23, is configured in the bottom stack BS ofthe force sensor FS. A pair of coplanar electrodes 241, 242 isconfigured on the bottom side of the bottom piezo layer 23, and thebottom substrate 25 is configured on the bottom side of the coplanarelectrodes 241, 242.

The top stack TS is comprised of a top substrate 20, and an auxiliarymetal 21B in sequence. The auxiliary metal 21B is an auxiliary metal forelectricity conductance when the force sensor FS is depressed. Thebottom stack BS is comprised of a piezo layer 23, a pair of coplanarelectrodes 241, 242, and a bottom substrate 25 in sequence.

FIG. 10B shows a side view of FIG. 10A. The first spacer S1 isconfigured between the top stack TS and the bottom stack BS andconfigured in the right side of the force sensor FS. A first gap G1 isconfigured between the top stack TS and the bottom stack BS. The firstspacer S1 has a top end connected to the auxiliary metal 21B of the topstack TS and has a bottom end connected to the bottom piezo layer 23 ofthe bottom stack BS.

FIGS. 11A˜11B shows a ninth embodiment according to the presentinvention.

FIG. 11A shows a modified embodiment to the first embodiment. FIG. 11Ashows a front view of the modified embodiment where a single piezolayer, a top piezo layer 22, is configured in the force sensor FS. Apair of coplanar electrodes 241, 242 is configured on the top side ofthe bottom substrate 25 of bottom stack BS in the force sensor FS.

The top stack TS is comprised of a top substrate 20 and a top piezolayer 22. The bottom stack BS is comprised of a pair of coplanarelectrodes 241, 242, and a bottom substrate 25 in sequence.

FIG. 11B shows a side view of FIG. 11A. The first spacer S1 isconfigured between the top stack TS and the bottom stack BS of the forcesensor FS. A first gap G1 is configured between the top stack TS and thebottom stack BS. The first spacer S1 has a top end connected to the toppiezo layer 22 of the top stack TS and has a bottom end connected to thepair of coplanar electrodes 241, 242 of the bottom stack BS.

FIGS. 12A˜12B shows a tenth embodiment according to the presentinvention.

FIG. 12A shows a modified embodiment to the first embodiment. FIG. 12Ashows a front view of the modified embodiment where a single piezolayer, a top piezo layer 22, is configured in the force sensor FS. Apair of coplanar electrodes 241, 242 is configured on the top side ofthe bottom substrate 25 of bottom stack BS in the force sensor FS.

The top stack TS is comprised of a top substrate 20, an auxiliary metal21B, and a top piezo layer 22 in sequence. The auxiliary metal 21B is anauxiliary metal for electricity conductance when the force sensor FS isdepressed. The bottom stack BS is comprised of a pair of coplanarelectrodes 241, 242, and a bottom substrate 25 in sequence.

FIG. 12B shows a side view of FIG. 12A. The first spacer S1 isconfigured between the top stack TS and the bottom stack BS of the forcesensor FS. A first gap G1 is configured between the top stack TS and thebottom stack BS. The first spacer S1 has a top end connected to the toppiezo layer 22 of the top stack TS and has a bottom end connected to thepair of coplanar electrodes 241, 242 of the bottom stack BS.

FIGS. 13A˜43B shows a tenth embodiment according to the presentinvention.

FIG. 13A shows a modified embodiment of the force sensor FS. A printedcircuit board 26 is configured on the bottom side of the force sensorFS. The top stack TS is comprised of a top substrate 20, a top electrode21, and a top piezo layer 22 in sequence. The bottom stack BS iscomprised of a bottom piezo layer 23 and a printed circuit board 26 insequence. A conductive contact C3 is configured on the top side of theprinted circuit board 26. The conductive contact C3 is covered by thebottom piezo layer 23.

A third spacer S3 is configured between the top stack TS and the bottomstack BS. A fourth gap G4 is configured between the top stack TS and thebottom stack BS. The third spacer S3 is configured in the right side ofthe force sensor FS. The third spacer S3 and has a top end connected tothe top piezo layer 22 of the top stack TS, and has a bottom endconnected to the bottom piezo layer 23 of the bottom stack BS.

FIG. 13B shows a depressed status of the embodiment of FIG. 12A.

FIG. 13B shows that the left side of the top stack TS is cantileveredfrom the bottom stack BS. When the force sensor FS is depressed from thetop side, the left side of the top stack TS moves down using the thirdspacer S3 as a fulcrum.

FIGS. 14A˜14B shows an eleventh embodiment according to the presentinvention.

FIG. 14A shows a modified embodiment to the embodiment of FIG. 13A witha different position of the third spacer S3. The third spacer S3 isconfigured between the top stack TS and the bottom stack BS. A fourthgap G4 is configured between the top stack TS and the bottom stack BS.The third spacer S3 is configured in the right side of the force sensorFS. The third spacer S3 and has a top end connected to the top substrate20 of the top stack TS, and has a bottom end connected to the printedboard 26 of the bottom stack BS.

FIG. 14B shows a CC′ section view of the embodiment FIG. 14A.

FIG. 14B shows that the third spacer S3 is configured in the right sideof the force sensor FS.

FIG. 15 shows a twelfth embodiment according to the present invention.

FIG. 15 shows a modified embodiment to the embodiment of FIG. 13A with adifferent position of the third spacer S3. The third spacer S3 isconfigured between the top stack TS and the bottom stack BS of the forcesensor FS. The four gap G4 is configured between the top stack TS andthe bottom stack BS. The third spacer S3 has a top end connected to thetop piezo layer 22 and has a bottom end connected to the printed circuitboard 26. The top stack TS is cantilevered from the bottom stack BS.

FIG. 16 shows a thirteenth embodiment according to the presentinvention.

FIG. 16 shows a modified embodiment to the embodiment of FIG. 13A with adifferent position of the third spacer S3. The third spacer S3 isconfigured between the top stack TS and the bottom stack BS andconfigured in the right side of the force sensor FS. The four gap G4 isconfigured between the top stack TS and the bottom stack BS. The thirdspacer S3 has a top end connected to the top substrate 20 of the topstack TS and has a bottom end connected to the bottom piezo layer 23 ofthe bottom stack BS. The top stack TS is cantilevered from the bottomstack BS.

FIG. 17 shows a fourteenth embodiment according to the presentinvention.

FIG. 17 shows that a force sensor 30 is configured with a bottom switchSW. A first conductive contact C1 is configured on the bottom side ofthe force sensor 30. A second conductive contact C2, aligned with thefirst conductive contact C1, is configured on a top side of a printedcircuit board 26. The force sensor 30 with the first conductive contactand the printed circuit board 26 with the second conductive contact C2forming the bottom switch SW. The first conductive contact C1 isconfigured in one of the two states:

(1) slightly touching the second conductive contact C2 without turningon the bottom switch SW, and

(2) slightly apart from touching the second conductive contact, and

a fourth spacer S4 is configured between the force sensor 30 and theprinted circuit board 26 and configured in the right side of the forcesensor 30. When the force sensor 30 is depressed from the top side, theleft side of the force sensor 30 moves down so that the first conductivecontact C1 touches the second conductive contact C2 firmly to turn onthe bottom switch SW.

The piezo layers 22, 23 disclosed in this invention is made of amaterial selected from the group consisting of piezo-electric material,triboelectric material, resistive material, and dielectric material

While several embodiments have been described by way of example, it willbe apparent to those skilled in the art that various modifications maybe configured without departs from the spirit of the present invention.Such modifications are all within the scope of the present invention, asdefined by the appended claims.

REFERENCE NUMBERS

-   20 top substrate-   21 top electrode-   21B auxiliary metal-   22 top piezo layer-   23 bottom piezo layer-   24 bottom electrode-   241, 242 coplanar electrodes-   25 bottom substrate-   26 printed circuit board-   30 force sensor-   61 pen tip-   G1 first gap-   G2 second gap-   G3 third gap-   G4 fourth gap-   C1 first conductive contact-   C2 second conductive contact-   C3 third conductive contact-   S1 first spacer-   S2 second spacer-   S3 third spacer-   S4 fourth spacer-   SW switch

What is claimed is:
 1. A cantilever force sensor, comprising a topstack, a bottom stack, a first spacer, a bottom switch, and a secondspacer, wherein the first spacer is configured, in a thickness directionof the force sensor, between the top stack and the bottom stack, and isconfigured in a first side of the force sensor, a second side, oppositeto the first side, of the top stack, is cantilevered from the bottomstack, in response to the top stack being depressed toward the bottomstack, the second side of the top stack moves down using the firstspacer as a fulcrum, one of the top stack and the bottom stack is afirst stack, another of the top stack and the bottom stack is a secondstack, the first stack comprises: a first substrate, a first piezolayer, and a first electrode between the first substrate and the firstpiezo layer in the thickness direction, the bottom switch comprises: afirst conductive contact configured on a bottom side of the bottomstack; a second conductive contact aligned with the first conductivecontact, and configured on a top side of a third substrate, and thesecond spacer is configured between the bottom stack and the thirdsubstrate in the thickness direction, and configured in the first sideof the force sensor.
 2. The cantilever force sensor as claimed in claim1, wherein the third substrate is a printed circuit board.
 3. Thecantilever force sensor as claimed in claim 1, wherein the firstconductive contact and the second conductive contact are configured inthe second side of the force sensor.
 4. The cantilever force sensor asclaimed in claim 3, wherein in a state where the top stack is notdepressed toward the bottom stack, the first conductive contact slightlytouches the second conductive contact without turning on the bottomswitch, and in response to the top stack being depressed toward thebottom stack, the first conductive contact is caused to touch the secondconductive contact firmly to turn on the bottom switch.
 5. Thecantilever force sensor as claimed in claim 3, wherein in a state wherethe top stack is not depressed toward the bottom stack, the firstconductive contact is slightly apart from the second conductive contact,and in response to the top stack being depressed toward the bottomstack, a second side opposite to the first side of the bottom stackmoves down using the second spacer as a fulcrum and causes the firstconductive contact to touch the second conductive contact firmly to turnon the bottom switch.
 6. The cantilever force sensor as claimed in claim1, wherein the second stack comprises: a second substrate, a secondpiezo layer, and a second electrode between the second substrate and thesecond piezo layer in the thickness direction, and along the thicknessdirection, the first spacer overlaps the first substrate and the secondsubstrate, without overlapping the first electrode, the first piezolayer, the second electrode and the second piezo layer.
 7. Thecantilever force sensor as claimed in claim 6, wherein as seen along thethickness direction, the first spacer has a shape of a segment of acircle.
 8. The cantilever force sensor as claimed in claim 1, whereinthe second stack comprises: a second substrate, a second piezo layer,and a second electrode between the second substrate and the second piezolayer in the thickness direction, and along the thickness direction, thefirst spacer overlaps the first substrate, the first electrode, thefirst piezo layer and the second substrate, without overlapping thesecond electrode and the second piezo layer.
 9. The cantilever forcesensor as claimed in claim 1, wherein along the thickness direction, thefirst spacer overlaps the second spacer.
 10. The cantilever force sensoras claimed in claim 9, wherein the second stack comprises: a secondsubstrate, a second piezo layer, and a second electrode between thesecond substrate and the second piezo layer in the thickness direction,and along the thickness direction, the second spacer overlaps the firstsubstrate, the first electrode, the first piezo layer, the secondsubstrate, the second electrode and the second piezo layer.
 11. Acantilever force sensor, comprising a top stack, a bottom stack, and afirst spacer, wherein the first spacer is configured, in a thicknessdirection of the force sensor, between the top stack and the bottomstack, and is configured in a first side of the force sensor, a secondside, opposite to the first side, of the top stack, is cantilevered fromthe bottom stack, in response to the top stack being depressed towardthe bottom stack, the second side of the top stack moves down using thefirst spacer as a fulcrum, the top stack comprises: a top substrate, atop piezo layer, and a top electrode between the top substrate and thetop piezo layer in the thickness direction, the bottom stack comprises:a printed circuit board having, on a top side thereof, a conductivecontact, and a bottom piezo layer on the top side of the printed circuitboard, wherein the bottom piezo layer is wider than the conductivecontact and covers the conductive contact.
 12. The cantilever forcesensor as claimed in claim 11, wherein along the thickness direction,the first spacer overlaps the top substrate and the printed circuitboard, without overlapping the top electrode, the top piezo layer, theconductive contact and the bottom piezo layer.
 13. The cantilever forcesensor as claimed in claim 12, wherein as seen along the thicknessdirection, the first spacer has a shape of a segment of a circle. 14.The cantilever force sensor as claimed in claim 11, wherein along thethickness direction, the first spacer overlaps the top substrate, thetop electrode, the top piezo layer, the printed circuit board and thebottom piezo layer.
 15. The cantilever force sensor as claimed in claim11, wherein along the thickness direction, the first spacer overlaps thetop substrate, the top electrode, the top piezo layer, the printedcircuit board, without overlapping the bottom piezo layer.
 16. Thecantilever force sensor as claimed in claim 11, wherein along thethickness direction, the first spacer overlaps the top substrate, theprinted circuit board and the bottom piezo layer, without overlappingthe top electrode and the top piezo layer.
 17. A cantilever forcesensor, comprising a top stack, a bottom stack, and a first spacer,wherein the first spacer is configured, in a thickness direction of theforce sensor, between the top stack and the bottom stack, and isconfigured in a first side of the force sensor, a second side, oppositeto the first side, of the top stack, is cantilevered from the bottomstack, in response to the top stack being depressed toward the bottomstack, the second side of the top stack moves down using the firstspacer as a fulcrum, the top stack comprises: a top substrate, a toppiezo layer, and a top electrode between the top substrate and the toppiezo layer in the thickness direction, the bottom stack comprises: abottom substrate, and a bottom piezo layer on a top side of the bottomsubstrate, along the thickness direction, the first spacer overlaps thetop substrate and the bottom substrate, without overlapping the topelectrode, the top piezo layer and the bottom piezo layer, and as seenalong the thickness direction, the first spacer has a shape of a segmentof a circle.
 18. The cantilever force sensor as claimed in claim 17,wherein at least one of the top piezo layer or the bottom piezo layer ismade of a material selected from the group consisting of piezo-electricmaterial, triboelectric material, resistive material, and dielectricmaterial.
 19. The cantilever force sensor as claimed in claim 17,further comprising: a bottom switch which comprises: a first conductivecontact configured on a bottom side of the bottom stack; a secondconductive contact aligned with the first conductive contact, andconfigured on the top side of a third substrate; and a second spacerwhich is configured between the bottom stack and the third substrate inthe thickness direction, and configured in the first side of the forcesensor, wherein the first conductive contact and the second conductivecontact are configured in the second side of the force sensor, in astate where the top stack is not depressed toward the bottom stack, thebottom switch is not turned on, and in response to the top stack beingdepressed toward the bottom stack, the first conductive contact touchesthe second conductive contact to turn on the bottom switch.
 20. Thecantilever force sensor as claimed in claim 17, wherein the bottomsubstrate is a printed circuit board having, on the top side thereof, aconductive contact, and the bottom piezo layer is wider than theconductive contact and covers the conductive contact.